For the first time in 360 years, compass needles at the Royal Observatory Greenwich in England will point toward true North. But why weren’t they pointing there in the first place?
Earth has two North poles: geographic or true North and geomagnetic North. In most cases, compasses don’t actually point toward the geographic or true North Pole. They instead point toward Earth’s geomagnetic North Pole, an ever-shifting location on the Earth’s surface. The space between true North and what compasses recognize as geomagnetic North is called the angle of declination. As the two locations move closer, that angle gets smaller.
Compass needles in Greenwich will finally point toward true north because the line of zero declination, where true and geomagnetic north align—also called the agonic—has been shifting west.
“This marks the first time since the observatory’s creation that the geographic and geomagnetic coordinate systems have coincided at this location,” geomagnetism scientist Ciaran Beggan of the British Geological Survey told the Guardian. She suspects that this alignment will only last for a few weeks.
Earth’s liquid iron core is responsible for the dynamic magnetic field that surrounds our planet. Geologists have found evidence to suggest that throughout geologic history, our poles have actually switched. The ever-shifting geomagnetic North has picked up the pace in recent years, sometimes traveling as far as 55 kilometers in a year and has thrown off navigation systems around the world. These changes have been so abrupt, that scientists had to update the World Magnetic Model in January just to keep up. Due to this year’s government shutdown, they had to delay the process.
Eventually, as the agonic continues to shift west, the compass needle will point further east. Sorry, Greenwich, but enjoy this brief moment of synchronicity while it lasts.
Source: The Guardian/Popula Mechanics.